The invention relates to a method for controlling an electronic line-scan camera, which has at least two lines with light-sensitive pixels, by means of external trigger signals.
It is known to scan continuous production processes or moving objects optically by means of line-scan cameras. Here, the camera and the object move relative to each other, with the motion taking place perpendicular to the sensor lines. Usually, the process takes place such that a trigger signal is generated as a function of the motion of the object, with the electronic camera being triggered by this trigger signal at certain sections of the object or certain times. A linear image is generated. Through successive linear scanning and assembly of several successive image lines in series, the entire object can be scanned and imaged.
For line-scan cameras with only one line, a trigger signal triggers exposure of the entire line, and then the image information is output. In principle, the control of such a line-scan camera presents no problems. Each line is allocated to a certain linear area on the object to be scanned. Control is performed such that the image lines are scanned at identical spatial intervals. Therefore, the spatial resolution is independent of the relative speed between the object and camera. The function of the trigger consists in the correct alignment of the camera to the relative motion between the camera and object. It must be guaranteed that the camera records an image at each trigger signal. Otherwise distortion could be generated. For optimal alignment, an overall image with isotropic resolution can be assembled line by line.
In line-scan cameras, sometimes multiple-line sensors are also used. These feature a predetermined number of sensor lines. Here, all of the lines are exposed simultaneously according to an external trigger signal. Usually a wider image area is detected than in a single-line image sensor. For the same spatial resolution, it would then be necessary to generate farther trigger signals spaced farther apart. However, because the trigger signals are generated external to the camera on the object side, an arbitrary use of such electronic cameras is not always easily possible.